I am struggling to understand bootstrapping the spot curve based on euroswaps. These contracts have a fixed leg paying an annual rate and a variable leg paying either euribor 3m 4 times a year or euribor 6m 2 times a year.
First of all I would like to know which is the swap to be used, fixed vs. 3m or 6m? Then to bootstrap the zero curve, I don’t quite follow the bond equivalence. In a swap with the same payment frequency I understand that the fixed leg is equivalent to a bond priced at par paying the rate as coupon. This equivalence does not seem valid to me though when the payment schedule is not the same on both legs.